Neutron particle detection is a method for fissile nuclear material detection. Because neutrons have no electrical charge, their detection generally relies on their participation in nuclear reactions. Some neutron detectors include gas-filled tubes containing neutron-sensitive material, such as either 3He or BF3 gas, which reacts with neutrons to form secondary charged particles that can subsequently be detected through ionization. Such gas-filled proportional neutron detectors can be relatively expensive, relatively bulky, not mechanically rugged, and require a large amount of power to operate.